Labeling of phosphorothioate antisense oligonucleotides with yttrium-90

Novel yttrium-90 (Y-90)-labeled phosphorothioate antisense oligonucleotides were designed as a potential targeted radionuclide therapeutic agent for m alignant tumors. A 15-mer phosphorothioate antisense oligonucleotide, which was complementary to the translation start region of the N/myc oncogene mR NA, was conjugated with isothiocyanobenzyl ethylenediamine tetraacetic acid (SCN-Bn-EDTA), via a C-5-substituted deoxyuridine that had replaced a thym ine in the oligonucleotide, and was then labeled with Y-90-acetate. Followi ng purification, the radiochemical purity of the Y-90-Bn-EDTA-phosphorothio ate antisense oligonucleotides was estimated by 2.0% agarose gel electropho resis, and the specific hybridization of Y-90-Bn-EDTA-phosphorothioate anti sense oligonucleotide to a phosphorodiester sense oligonucleotide was inves tigated by 20% polyacrylamide gel electrophoresis in a cell-free system. Ra diochemical purity was 98.7 +/- 0.4 % at 72 h after labeling and 90.3 +/- 0 .9% after 72-h incubation with human normal serum. The Y-90-Bn-EDTA-phospho rothioate antisense oligonucleotide hybridized specifically to a complement ary phosphorodiester sense oligonucleotide. In conclusion, phosphorothioate antisense oligonucleotides can be labeled stably with 90Y using SCN-Bn-EDT A without loss of hybridization properties. NUCL MED BIOL 26;2: 219-243 199 9 (C) 1999 Elsevier Science Inc. All rights reserved.